Hi Emily, Visual Studio 2010 Express will support VS Tools. You can develop an Addin, but it has 2 limitations as far as I know.
1. You will not get the Dynamics GP Addin template automatically when you install VS Tools SDK. So you should be doing that manually by opening a Class Library project.
2. Attach to Process option will not be there for Express Editions and hence you can't debug your addin.
